The semiconductor light emitting element (LED element) using a nitride semiconductor such as GaN can emit UV light or blue light and also can emit white light by utilizing a florescent substance (phosphor). Such a semiconductor light emitting element is used for lighting equipment such as a lighting tool for a vehicle.
The LED element includes at least an optical semiconductor laminated layer and electrodes to apply an electric voltage to the optical semiconductor laminated layer. The optical semiconductor laminated layer has a structure stacking, for example, a n-type GaN layer, an active layer having a light emitting property and a p-type GaN layer. The electrodes contacts with the n-type and p-type GaN layers, respectively. The LED element is classified into a counter electrode type, a flip chip type, a junction down type, a via type, or the like, according to the difference of a structure of the electrodes, an arrangement position of the electrodes, or the like.
A material having high optical reflectance, for example, Ag or an Ag alloy can be generally used as the electrodes in order to enhance the light emitting efficiency (=light intensity of light emitted from a surface of the optical semiconductor laminated layer/light intensity in the active layer) of the LED element. However, the electrodes including Ag or the like easily migrates, and causes problems on reliability such as electric short circuiting, leakage, or the like of the LED element.
It is desirable to provide a cap layer (migration suppressing layer) that covers the entire surface of the electrodes in order to suppress the migration of the electrodes including Ag or the like. The cap layer includes, for example, refractory metal, a metal nitride, or the like (for example, Japanese Laid-open Patent Publication No. 2008-192782).